Control for electron tubes



Jan. 19, 1932. c. STANSBURY ET AL 1,341,765,

CONTROL FOR ELECTRON TUBES 1 Filed on. so, 1950 8 BMW fix 12 'Er Et QQ/V/WXX" BWMX E & M +mM 4 x WWW Patented Jan. 19, 1932 UNITED STATES PATENT OFFICE CARROLL STANSBURY, F WAUWA'IOSA, AND GLENDON C. BROWN, OF MILWAUKEE, WISCONSIN, ASSIGNORS TO CUTLEBr-HA'MMER, INCL, OF MILWAUKEE, WISCONSIN,

A CORPORATION OF DELAWARE CONTROL FOR ELECTRON TUBES Application filed October 30, 1930.- Serial No. 492,220.

This invention relates to the control of certain gaseous electron discharge tubes of the type in which discharge between the anode and cathode is initiated when the potential of the grid with respect to the cathode exceeds a critical positive or negative value. Such tubes are usually provided with a very small anode surface.

In another aspect the invention relates to the use of electron-tubes of the above described character in connection with a phase failure and phase reversal protective system such as described in our co-pending application, Serial No. 432,278, filed February 28, 1930.

An object of the invention is to provide means whereby a tube of the above described character will only respond when the grid potential with respect'to the cathode is above the critical positive; value and will not respond when the voltage is below the critical negative value or vice versa.

Another object is to provide improved means responsive to abnormal operating conditions in a polyphase circuit such as phase failure, phase reversal or unbalance of the voltages, using a tube of the character described heretofore.

other objects and advantages will hereinafter appear.

The accompanying drawings illustrate one embodiment of our invention.

Figure 1 shows our invention embodied in a phase failure and phase reversal protective system similar to that generally described and claimed in the above mentioned co-pending application.

Fig. 2 illustrates the relation between plate voltage and grid voltage of the type of tube matically-P'illustrates the invention as em-' 'ji ployed in connection with a three phase power supply system. A, B and Care the "tem .under different conditions of power suppl Re e rring to Fig. 1 the same diagramterminals o, f a power supply system in which the voltages between any two of the three lines are equal. A transformer having a primary winding 1 is connected between the lines A and B. The transformer has 9. voltage tap in the center of its primary windingand between such tap and the line C are connected in series the two non-inductive resistances 2 and 3. An electron tube 4 of the gaseous type having a cathode 5, an anode 6 and a grid 7 is connected in series with an electro-magnetic relay 8 between the mid tap of the winding 1 and the line B. The transformer is also equipped with a secondary winding 9 which is connected between the point intermediate of the resistances 2 and 3 and the grid 7. A rectifier 10 of any well known type having preferably a low impedance has a cathode 12 which is connected tothe grid 7 while an anode 11 of said rectifier is connected to the cathode 5.

The tube 4 is of a type in which discharge between the anode and cathode is initiated when the potential of the grid with respect to the cathode is either above a certain ositive or below a certain negative value. his critical value at which the tube responds varies with different potentials between the anodes and cathodes and depends upon the construction of the tube.

Fig. 2 diagrammatically illustrates the relation between the grid potential E and the anode potential E of the tube such as em ployed in the present system. The tube conducts current only when the anode is positive with respect to the cathode and for an instantaneous positive value of the voltage E the tube will initiate a discharge only if the grid potential E with respect to the cathode is above or below the values within the shaded area of the diagram Fig. 2. After the flow of current during the positive half cyele has once been initiated, current will,

Of course, flow during the remainder of such "half cycle and the tube will act in substantially the same manner as all gaseous discharge tubes.

In the present system, initiation of current flow during the positive half cycle is controlled by controlling the-phase relation between the grid voltage and the plate or anode yes voltage during the positive half cycle so that under normal conditions the voltage impressed upon the grid has a sufliciently high positive value at the beginning oirthe posinormal conditions, the grid potential during the positive half cycle of the plate voltage might attain a sufficiently low negative value to start current fiow through the tube.

In order to avoid this, the rectifier 10 is connected between the. cathode and the grid of the tube in such a manner that practically no current can flow from the grid, to the cathode through the rectifier circuit, while the flow of current in the opposite direction over the same path is substantially unobstructe'd, so that when the grid potential tends to attain a negative value with respect to the cathode, current flows from -the cathode through the rectifier to the grid and maintains the latter at a negative value withrespect to the cathode which difi'ers only slightly from zero and thus prevents the initiation I of a discharge through the tube.

The apparatus functions in the following manner:

Assume that the voltages of the power supply system are balanced and that the normal phase rotation of the same is counter-clock wise. By referring to Fig. 3, it will be apparent that the voltage between the anode 6 and the cathode 5 may be represented by the horizontal vector E while the grid voltage E,; has two components, namely, the voltage drop through the resistance 2 which may be represented by the vector E and the*voltage induced in the secondary winding 9 which may be represented by the vector E If the voltages in the system are assumed to be rotating counter-clockwise as indicated by the arrow, the instantaneous voltages of the tube may be represented as in Fig. 4, Where E is the instantaneous plate voltage'and E the instantaneous grid voltage.' The dotted lines E and E show the critical voltages beyond which the voltage of the grid must fall in order to start anode current during the half cycle of positive anode voltage, it being understood that once the current has started during thepositive half cycle, it cannot be stopped by any change in the grid voltage.

If the grid voltage, which i's'represented by the curve E is positive during the beginning of the positive half cycle and its value is above the critical value as represented by Fig. 2, current starts .to flow just after the beginning of this half cycle and c any subsequent change in the instantaneous grid voltage has no further effect. upon the functioning of the tube and hence upon the fages when a short circuit existsbetween the amount of energy passing through the translating device 8. This translating device may be,- for instance,'a relay equipped with contacts for the control of other instrumentalities and the eflective current corresponding to E andwhich passes through'the relay under normal conditions is sufficient to cause it to close such contacts.

If now the phase rotation of the supply lines is reversed, the volta e relations are modified as illustrated in' iagram Fig. 5. Fig. 6 shows the relation of the instantaneous grid and plate voltages and it is apparent that during practically the entire positive half eycle' the grid voltage isslightly negative but less than the critical value so .that the tube beconiesconducting only during the very last fraction" of this half cycle or not at all with. the result that thefleilective current which passes through the relay 8 is re:

" duced to a sufiici'ently small value to cause it to open its contacts and thus cause theconnected controlling ,inst umentalities to res ond.

ig. 7 represents the relation of the voltlines C and B, while.

Fig. 8 isea diagram fertile case where a short circuit takes placebet'ween-the lines C and A; In both cases the instantaneous grid voltage is negativeduring the positive half c debut on accountcof the inter-position of, t e rectifier 10 between the cathode and the grid this grid'voltage is of such a small value as to prevent theinitiation of discharge between the main' electrodes and thus the relay receives no current. I

It will be obvious that "the system'illustrated in Fig. 1 may also'b'e applied. to a power s pply having a diflerent number of hases t an that shown and/it will further e apparent that the rectifier '10 may be employed in connection with a gaseous dis-L charge tube of the character described for other purposes where it is desired to reduce the ne ative gr'd voltage which would-other- Wise 0 tain without said rectifier.

It will further be clear that the connections of the rectifier may be reversed so that the negative grid voltage which is o rrnally impressed upon the. tube is not materially modified there y whereas the positive grid voltage during the other half cycle is reduced to a value which departs only slightly from zero unilaterally' conducting device associated with said element and one of the main electrodes of said tube to prevent the potential impressed on said element attainingone such critical value, whereby initiation of discharge of said tube is rendered dependent upon the control voltage attaining the other critical value.

2. The combination with a gaseous discharge tube having a grid which initiates discharge between the main electrodes of said tube when'said grid is subjected to a voltage above a critical positive or below a critical negative value and a suitable potential difference is impressed upon said main electrodes, of a rectifier connected between said grid and one of the main electrodes of said tube to prevent the potential impressed on said grid attaining one such critical value,

whereby initiation of discharge of said tube; Said tube b ti ll t "th b is rendered dependent upon the control voltage attaining the other critical value.

3. The-combination of a current supply, a translating device, a gaseous discharge tube in circuit with said supply and said translating device and having a grid which initiates discharge between the main elcctrodesof said tube when said grid is subjected to a voltage above a critical positive or below a critical negative value and a rectifier connected between said grid and one of the main eleccritical value.

4. The combination of a current supply, a translating device, a gaseous discharge tube in circuit with said supply and said translating device and having a grid which initiates discharge between the main electrodes of said tube when said grid is subjected to a voltage above a critical positive or below a critical negative value, means for impressing upon said grid a control voltage responsive to a condition of power supply and a rectifier connected between said grid and one of the main electrodes of said tube to prevent the potential impressed on said grid attaining one of said critical values, whereby initiation of discharge of said tube is rendered dependent upon the control voltage attaining the other critical value.

5. The combination of an alternating current supply, a translating device, a unilaterally conducting' gaseous discharge tube in circuit with said supply and said translating device and having a grid which initiates discharge between the mainelectrodes of said tube during positive half cycles of said supply when said grid is subjected to a voltage above a critical positive or below a critical negative value, means for impressing upon said grid a control voltage responsive to a condition of power supply, and a rectifier connected between said grid and one of the main electrodes of said tube to prevent the potential impressed on said grid attaining one of said critical values, whereby initiation of discharge of said tube is rendered dependent upon the control voltage attaining the other critical value.

6. In combination a polyphase current system, a gaseous electron tube connected to said system and having a grid which initiates discharge between the' main electrodes of said tube during positive half cycles of said supply when said grid is subjected to a voltage above a critical positive or below a critical negative value, means to normally impress upon the grid a voltage which lagsa given anglev with respect to the anode voltage soas to insure starting of the discharge current ginning-ofthepositive half cycle of-the impressed voltage and'to reduce said lag to thereby. stop said discharge, and a rectifier connected between said grid and one of the main electrodes of the tube toprevent the potential impressed upon said grid attaining one of said critical values whereby initiation of discharge .of said tube is rendered de-' pendent upon the control voltage attaining the other critical value.

7. In combination a polyphase circuit, a load circuit, a vapor electric device provided with a-cathode and an anode connected between certainphases of said polyphase'and said load circuit anda grid also connected to said polyphase circuit and arranged to .con-

trol the current transmitted between said cathode and anode, said grid being capable of' initiating discharge between the main-electrodes of said tube when subjected to a voltage above a critical positive or below a critical negative value, such connection being adapted to normally impress upon said electrode a voltage which lags a given angle behind the voltage of the alternating current circuit so as to insure starting of the current between said cathode and anode at the beginning of the positive half cycle of the voltage of the alternating current circuit and to reduce the lag of'said control voltage to thereby p revent such starting, and a rectifier connected between said grid and one'of the main electrodes of said tube to prevent the potential impressed upon said grid attaining one of said critical valueswhereby initiation of discharge of said tube is rendered dependent upon the control voltage attaining the other critical value. I

8. In combination a polyphase circuit, a translating device, a vapor electric device provided with a cathode and an anode con nected in series with said translating device to said circuit so as to receive space current therefrom,said vapor device being provided with a gridarranged to initiate discharge between the main electrodes of said tube during positive half cycles of said tube when said grid is subjected to a voltage above a critical positive or below a critical negative value, said electrode being connected to the circuit so as to be normally subjected to a potential which lags a given angle behind the cathode potential, such lag being redueed'by abnormal current and voltage conditions in* the circuit, and a rectifier connected between said grid and one of the main electrodes of the tube to prevent the potential impressed on'said grid attaining one of said critical values whereby initiation of discharge of said tube is rendered dependent upon the control voltage attaining the other critical value.

In Witness whereof, We have hereunto sub scribed our names. l

CARROLL STANSBURY. GLENDON G. BROWN. 

